Analytical and Numerical Calculation of the Orifice Minimum Temperature Due to Joule - Thomson Effect

Mohammed Mohammed Said

doi:10.11648/j.fm.20170305.11

Abstract

High pressure drop generated by a restriction orifice may result in a very low temperature, which can affect the piping material and may cause catastrophic piping failure if the operating temperature becomes lower than the minimum design temperature. This minimum design temperature is stated by piping ASME B31.3 code as -48°C. In such piping research branch, there has been relatively little investigation of very low temperature effect on pipelines. As well as, sizing the orifice with implementing temperature control to match piping material has a few analytical explanations, particularly in investigating the influence of Joule - Thomson effect on piping damage. Most commercial orifice sizing software ignore Joule - Thomson effect even though in choked flow condition. The objective of the present research is to compare a derived analytical equation with 3-D computational calculations by using ANSYS 16.0 for Joule - Thomson temperature drop through the orifice. As well as correlate the analytical equation to be safely considered as a good prediction tool for the lowest temperature at orifice throat instead of misleading ISO 5761 fully developed Joule - Thomson temperature drop. The analytical equation correlation has been carried out based on non-linear regression by grouping flow conditions, fluid properties, and orifice geometry, for minimum temperature prediction at orifice Vena-contracta. The numerical temperature differences in the fully developed flow regime after the office have been compared with EN ISO 5761-Part 3 Joule - Thomson temperature drop equation. Three orifices with β ratios, 0.3, 0.4, and 0.5 have been chosen for such study and numerical simulations have be carried out using k-e and k-ω turbulence models. As a corollary of this study, it was concluded that the k-e and k-ω models predict well both the flow and the fully developed temperature drop as compared with ISO 5761 equations. The errors are generally accepted at all conditions and both values give good agreement. The derived equation successfully predicts the lowest minimum temperature at Vena-contracta and can supersede ISO 5761-Part 3 Joule - Thomson temperature drop at fully devolved region.

Highlights

Restriction orifice is common used in gas processing facilities, which may have flare or vent systems that occasionally handle cold relief flows
To analyze the relevant relation between both the temperature drop due to Joule - Thomson effect at fully developed condition (i.e. 6D after the orifice ) by EN ISO Equation (4) and Joule - Thomson effect by proposed Equation (7) at 1⁄2 D after the orifice with the numerical results, the results of this study are summarized in Table 1, Table 2, and Error! Reference source not found
The theoretical EN ISO 5761 Joule Thomson temperature drop at fully developed zone is firstly validated by ANSYS 16.0

Summary

Introduction

Restriction orifice is common used in gas processing facilities, which may have flare or vent systems that occasionally handle cold relief flows. As the fluid flow passes through the restricted orifice, a significant pressure drop is created across the orifice plate which results in high pressure loss [1]. The pressure drop through orifices always undergoes several research studies. From such studies is the investigation of the pressure drop through orifices for single and two phase flow [2]. A restriction orifice with high-pressure drop leads to a reduction in the temperature of the flowing gas downstream the orifice and to the adjacent piping walls and possibly to a temperature below the ductile - brittle transition temperature of the steel from which the piping is fabricated. The orifice upstream portion, in industrial piping design of Mohammed Mohammed Said et al.: Analytical and Numerical Calculation of the Orifice Minimum Temperature Due to

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Conclusion